This invention relates generally to the field of automobiles, and in particular, to a system and method of controlling the coastdown of an automobile.
Conventional automobiles typically include speed control software that controls the speed of the engine under various driving conditions. This software may consist of a number of operating modes. For example, such software may include a xe2x80x9ccoastdownxe2x80x9d control mode that controls the rate of deceleration of the vehicle, which prevents engine stalls in low speed driving scenarios such as those encountered in parking lots and improves the driveability of the vehicle. Typically, the coastdown control mode is active when the throttle is closed and the vehicle is moving. The speed control software may also include an idle speed control mode that controls the speed of the engine under idle conditions. In operation, the speed control software transitions from the coastdown control mode (while the vehicle is decelerating) to the idle speed control mode (after the speed of the vehicle drops below a predetermined vehicle speed calibration).
Conventional coastdown control systems typically employ a mass airflow MAF-based methodology for the coastdown control mode. The MAF-based methodology is generally a closed loop control algorithm based on a desired engine mass airflow. However, it does not have MPH feedback to control the deceleration rate directly, and it does not have engine speed (i.e. RPM) feedback to control engine speed sags or droops, which may lead to engine stalls.
There are many other disadvantages to these conventional coastdown control systems. For example, there are typically many variables that must be considered in determining the desired MAF. In particular, there are many open loop terms that are required to determine the desired MAF in order to take into account the various engine load and operational conditions. This in turn results in the need for a significant amount of software and memory (i.e. RAM and ROM) to implement this control strategy, which increases the cost of the overall control system considerably. Moreover, a tremendous amount of time is required to calibrate the large number of variables that must be taken into account. This also adds considerable cost to the control system. Finally, the transition between the coastdown mode and the idle speed control mode is very complex because the coastdown mode is typically MAF based while the idle speed control is typically engine speed (RPM) based. Any discontinuities between these modes can lead to engine stalls. This problem is compounded if any loads to the engine are applied simultaneously.
Accordingly, it would be desirable to have a system and method of controlling the coastdown of a vehicle that overcomes the disadvantages described above.
One aspect of the invention provides a method of controlling the coastdown of a vehicle. A base engine speed reference is determined. A speed of the vehicle is sensed, and a target engine speed is generated from the base engine speed reference and the speed of the vehicle. An actual engine speed is sensed. A desired throttle position is determined by a speed controller based on a difference between the target engine speed and the actual engine speed. A desired spark advance is determined for the engine by the speed controller based on the difference between the target engine speed and actual engine speed. A gear shift of a transmission may preferably be sensed, and the desired throttle position may preferably be adjusted in response to the gear shift. A turbine speed of a transmission may also be sensed, and the target engine speed may be generated from the base engine speed reference, the speed of the vehicle, and the turbine speed. A gear of the transmission may also be sensed. The target engine speed may preferably be generated from the base engine speed reference, the speed of the vehicle, the turbine speed of the transmission, and the gear. A coolant temperature may preferably be sensed, and the base engine speed reference may be determined from the coolant temperature. The ambient air pressure may also be sensed, and the base engine speed reference may be determined from the ambient air pressure. Whether a desired deceleration rate is occurring based on the speed of the vehicle may be determined. An offset may preferably be generated if the desired deceleration rate is not occurring. The offset may preferably be applied to the target engine speed to achieve the desired deceleration rate. A coastdown turbine speed reference may preferably be generated as a difference between the turbine speed and a calibrated coastdown turbine speed reference. The coast down turbine speed reference may preferably be applied to the target engine speed to minimize a bump felt through the drivetrain and vehicle chassis.
Another aspect of the invention provides a method of controlling the coastdown of a vehicle. A transmission including a plurality of gears is provided. The transmission is operatively coupled to the engine, and a driveline is operatively coupled to the transmission. A throttle is in communication with the engine to regulate the amount of airflow to the engine. A base engine speed reference is determined. A speed of the vehicle is sensed from the driveline, and a turbine speed and a gear are both sensed from the transmission. A target engine speed is generated from the base engine speed reference, the turbine speed, the gear, and the speed of the vehicle. An actual engine speed is sensed, and a desired throttle position is determined by a speed controller based on a difference between the target engine speed and the actual engine speed. A desired spark advance for the engine is determined by the speed controller based on the difference between the target engine speed and actual engine speed. A gear shift from the transmission is sensed, and the desired throttle position is adjusted in response to the gear shift.
Another aspect of the invention provides a system for controlling the coastdown of a vehicle including a basic reference calculator that determines a base engine speed reference. Means for sensing a speed of the vehicle is provided. A reference trajectory generator is also provided that generates a target engine speed from the base engine speed reference and the speed of the vehicle. Means for sensing an actual engine speed is provided. A speed controller determines a desired throttle position based on a difference between the target engine speed and the actual engine speed and a desired spark advance for the engine based on the difference between the target engine speed and actual engine speed. A means for sensing a gear shift of a transmission may also be provided. A downshift feedforward controller adjusts the desired throttle position in response to the gear shift. A means for sensing a turbine speed of a transmission may also be provided so that the reference trajectory generator generates the target engine speed from the base engine speed reference, the speed of the vehicle, and the turbine speed. A gear of the transmission may be sensed so that the reference trajectory generator generates the target engine speed from the base engine speed reference, the speed of the vehicle, the turbine speed of the transmission, and the gear. A means for sensing a coolant temperature may preferably be provided wherein the basic reference calculator determines the base engine speed reference from the coolant temperature. A means for sensing ambient air pressure may also be provided wherein the basic reference calculator determines the base engine speed reference from the ambient air pressure.
Another aspect of the invention provides a program for controlling the coastdown of a vehicle. Computer readable program code determines a base engine speed reference and senses a speed of the vehicle. Computer readable program code generates a target engine speed from the base engine speed reference and the speed of the vehicle. Computer readable program code senses an actual engine speed and determines a desired throttle position based on a difference between the target engine speed and the actual engine speed. Computer readable program code determines a desired spark advance for the engine based on the difference between the target engine speed and actual engine speed. Computer readable program code may preferably sense a gear shift of a transmission and may adjust the desired throttle position in response to the gear shift. Computer readable program code may also preferably sense a turbine speed of a transmission, and generate the target engine speed from the base engine speed reference, the speed of the vehicle, and the turbine speed. Computer readable program code may preferably sense a gear of the transmission, and may preferably generate the target engine speed from the base engine speed reference, the speed of the vehicle, the turbine speed of the transmission, and the gear. Computer readable program code may preferably sense a coolant temperature, and may preferably determine the base engine speed reference from the coolant temperature. Computer readable program code may preferably sense ambient air pressure, and may preferably determine the base engine speed reference from the ambient air pressure.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.